Circuit arrangement for position and feed control of a hydraulic cylinder

Abstract

The object of the invention is to improve the position and feed or advance regulation of a hydraulic drive which is controlled by a proportional valve. In a first compensation circuit the flow characteristic of the proportional valve is linearized to obtain very small feed rates and a high control amplification. In a second compensation circuit the positioning error of the drive arising from the necessary overlapping of the proportional valve is compensated.

I claim: 
     
       1. A control circuit which is part of an arrangement for position and feed control of a hydraulic cylinder, the arrangement having a proportional valve with an overlap in its neutral position in which its passages close before the valve is fully in the neutral position for controlling fluid paths between the cylinder and a fluid source and a tank, the control circuit comprising: means for generating a control signal from a deviation between a common variable and a controlled variable,   a first compensation circuit for generating a position compensation signal when said proportion valve approaches the overlapping position,   means for summing said position compensation signal and said control signal, and   amplifier means for communicating an operating signal to said proportional valve in response to a summation of said position compensation signal and control signal, the operating signal directing the proportional valve to retain a remaining cross-section of said proportional valve opened before reaching its overlapping condition and until the control deviation is zero.   
     
     
       2. Control circuit according to claim 1, characterized in that the first compensation circuit can be tuned to provide different signals for the position of said proportional valve on either side of its neutral position. 
     
     
       3. Control circuit according to claim 1 further including a second compensation circuit for providing a non linear compensation signal to said proportional valve for effecting linear operation in the entire range the stroke of said proportional valve. 
     
     
       4. Control circuit according to claim 3, characterized in that the nonlinear compensation signal is added to the position compensation signal and the control signal in the summing means and a summation of the nonlinear compensation, position compensation, and control signals is communicated to the amplifier. 
     
     
       5. Control circuit according to claim 3, characterized in that the second compensation circuit outputs a digressive signal profile. 
     
     
       6. Control circuit according to claim 1, characterized in that the means for generating the control signal is a differentiating stage connected to the first compensation circuit. 
     
     
       7. Control circuit according to claim 3 characterized in that the second compensation circuit is made up of zener diodes which are connected into the feedback of an operational amplifier serving a differentiating stage. 
     
     
       8. Control circuit according to claim 3 characterized in that the control circuit further comprises an auxiliary circuit for affecting closure of the proportional valve before a desired position of the cylinder is reached. 
     
     
       9. Control circuit according to claim 8, characterized in that he auxiliary circuit is connected to the output of the second compensation circuit and opens a switch between the summing means and the amplifier connecting the summing means into said amplifier on reaching a predetermined control deviation from zero. 
     
     
       10. Control circuit according to claim 1, characterized in that the control circuit further comprises a programmable NC control with a proportional voltage output.